1. Field of the Invention
This invention relates to a color picture tube having an improved phosphor screen.
2. Description of the Related Art
In recent years, a color picture tube called "black matrix type color picture tube" is widely used, in which light absorbing layers fill a guard band region among phosphor dots constituting a phosphor screen. In this color picture tube, light absorbing layer 12 is formed in a predetermined region of panel 2 as shown in FIGS. 2 to 4. Phosphor layers 14 are formed in hole regions 13 partitioned by light absorbing layer 12. As is shown in FIG. 4, phosphor layers 14 not only exist in hole regions 13 but overlap light absorbing layers 12.
Since phosphor layers 14 partially overlap light absorbing layer 12, light emitted from overlap portion 14a of phosphor layer 14 is absorbed by light absorbing layer 12, not contributing to display. This inevitably prevents improvement on that brightness of the phosphor screen.
To overcome the drawback, a light absorbing layer having 5 to 40% light absorbance is used as proposed in, for example, Published Unexamined Japanese Patent Application No. 52-74274. This light absorbing layer allows passage of the light emitted from the overlap portion of the phosphor layer, thereby improving brightness. It is true that brightness of the phosphor screen can be improved by the light absorbing layer which transmits light. However, if the light transmittance of the light absorbing layer is too high, the ambient light reflectivity is also high, inevitably lowering the contrast. If the light transmittance is set low so as to suppress the outer light reflectivity, it is difficult to obtain sufficient brightness.